Apparatus and method for thermal and vibrational stress screening

ABSTRACT

Environmental screening of products is facilitated and enhanced by employing screening compartments to subject products to differing environmental conditions. Products can be simultaneously screened under various temperature, vibrational and other stimuli. Further, products are readily transported between screening compartments chambers in order to rapidly subject the products to differing screening conditions while minimizing energy wasted in heating or cooling elements not being screened. The present invention reduces the level of time, manual intervention and energy required in order to evaluate product tolerance to differing environmental conditions.

BACKGROUND OF THE INVENTION

The present invention relates generally to the screening of products forthe presence of latent defects which would be exposed by normal usageand transportation during the life of the products. More particularly,the present invention relates to a new and improved method forenvironmentally stress screening products, by subjecting the products tothermal and vibrational stimuli, optimally simultaneously. Otherstresses such as electric power cycling, voltage changes, and inputpower frequency variations may be introduced to the products beingscreened, and the products can be monitored to determine if the productsfunction and continue to function as expected. It has been found thatthese combined thermal and vibrational stimuli, when combined withsimultaneous rigorous functional monitoring, enable root causecorrective action to be implemented to remedy the cause of latentdefects uncovered during the screening. Environmental screening inaccordance with the present invention can lead to significant productquality improvements, production cost reductions, reduced warrantyrepair expense, increased customer satisfaction, and increased marketshare.

Applications of the current state of the art in environmental screeningis very energy, time, and effort intensive, thereby rendering suchscreening very expensive. Existing screening techniques utilizetemperature cycling within a chamber which, in more advanced cases, alsohas a product vibrating device within it. The chamber itself and thevibrating device act as thermal loads on the chamber, thus requitingmore energy to heat and cool the electronic product being tested throughthe desired thermal cycles. Both the vibrating device and the thermalloads react to temperature changes, radiating and/or absorbing thermalenergy in response to changes in ambient temperature. Accordingly,changing the temperature of the chamber and the vibrating devicenaturally requires more energy than if just the product were to becycled through temperature changes. In some cases, the chamber andvibrating device consume the majority of the energy costs to no usefulend. Additionally, cycling the chamber and vibrating device throughvarious temperature changes requires more time than if just the productwere to be cycled.

As an alternative to screening products by cycling them throughdifferent temperatures in a single, variable-temperature chamber,products may be successively moved into and subjected to multipletemperature-controlled chambers which are maintained at different fixedtemperatures. Existing "thermal shock chambers" shuttle products betweentemperature-controlled chambers to subject the products to differingextremes of temperature. However, when the chambers are opened or closedto insert and remove products being screened, thermal energy can beexchanged with adjacent chambers and/or the ambient environment, andenergy will be wastefully consumed in restoring the desired temperaturewithin the chambers. Further, manual intervention is required if theproducts to be screened must be connected to or disconnected fromvibrating devices or other testing devices, and additional thermalenergy will be lost to the ambient environment while the chambers areopen to allow the connections to be made.

Where screening for defects susceptible to vibration is desirable,energy efficiency concerns are magnified. If a temperature-controlledchamber is equipped with a vibrating device, such as a shaker table,when the chamber is heated and/or cooled, the vibrating device must alsobe heated or cooled. Accordingly, reaching and/or restoring the desiredtemperature in the chamber requires additional energy to heat and/orcool the vibrating device, as described above. Further, repeated heatingor cooling of the screening apparatus may have detrimental effects onthe reliability of the vibrating device due to material fatigue as wellas potentially nonuniform thermal expansion and contraction of parts andother effects, which may be detrimental to the operability of movingparts.

In sum, existing environmental screening systems consume energy and timeinefficiently. Existing systems also require manual intervention toconnect products to testing devices for testing vibrational and otherstimuli. It is because of these and other background considerations thatthe present invention has evolved.

SUMMARY OF THE INVENTION

General objectives of the present invention are to facilitate andenhance environmental screening of products under predetermined testingconditions, to provide more comprehensive screening and to makeenvironmental screening more efficient by reducing the energy, time, andmanual intervention required to undertake environmental screening.

One aspect of the present invention is to allow products to be morecomprehensively screened under multiple environmental stimuli includingtemperature changes, vibration, and other stresses. In accordance withthis aspect of the present invention, the apparatus and method of thepresent invention allow products to be simultaneously screened underthermal and vibrational stresses. Moreover, the present inventionisolates the source of the thermal stimuli from the source of thevibrational stimuli to minimize the energy wasted in heating or coolingitems not being tested.

In accordance with other aspects of the present invention, multiplescreening environments are maintained at differing temperatures tosubject products to differing extremes of temperature without heating orcooling the entire screening apparatus to test products at differenttemperatures. Further, products can be moved between screeningcompartments with little or no manual intervention so that the productscan be cost-effectively exposed to rapid changes in temperature. Thepresent invention also allows for connections of the products to be madeto vibrating devices and/or other testing devices, such as electronictesting devices, without manual intervention to allow the products to bescreened efficiently under vibrational and other stimuli.

A more complete appreciation of the present invention and its scope canbe obtained from understanding the accompanying drawings, which arebriefly summarized below, the following detailed description of apresently preferred embodiment of the invention, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of the screening apparatus of the presentinvention.

FIG. 2 is a vertical fragmentary section taken along line 2--2 of FIG. 1showing the interior of the divided screening compartments of theapparatus of the present invention.

FIG. 3 is an enlarged vertical fragmentary section taken along line 3--3of FIG. 2 showing the inside of a single divided screening compartmentof the apparatus of the present invention. FIG. 4 is a horizontalfragmentary section taken along line 4--4 of FIG. 3 showing the insideof a single testing chamber.

FIG. 5 is an enlarged fragmentary vertical section taken along line 5--5of FIG. 4 showing a portion of the vibrating device and transfermechanism of the apparatus of the present invention.

FIG. 6 is an enlarged fragmentary vertical section taken along line 6--6of FIG. 4 showing the transfer mechanism of the apparatus of the presentinvention.

FIG. 7 is an enlarged fragmentary vertical section of the valve chambertaken along line 7--7 of FIG. 3.

FIG. 8 is an enlarged fragmentary vertical section of the viewing windowtaken along line 8--8 of FIG. 3.

FIG. 9 is an enlarged fragmentary vertical section of the actuator armtaken along line 9--9 of FIG. 5.

FIG. 10 is an enlarged fragmentary side view of the actuator arm shownin FIG. 5 in a retracted condition.

FIG. 11 is an enlarged fragmentary plan view of the actuator arm shownin FIG. 5.

FIG. 12 is an enlarged fragmentary side view of the actuator arm shownin FIG. 5 similar to FIG. 10 with the actuator arm extended.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is intended primarily for use for environmentallystress screening products 20 to detect latent defects in the productthat can become apparent in vibrational and varying thermalenvironments. In the apparatus of the present invention, as best seen inFIGS. 1 and 2, products 20 to be screened are mounted onspecially-designed pallets 22, which are moved into the first of aseries of divided screening chambers or compartments 24 by an entryconveyor 26 and removed from the series of chambers 24 by an exitconveyor 28. The divided screening compartments 24 are each equippedwith a heating device 30, as shown in the first and last chambers 24 inFIG. 2, and/or a cooling device 32, as shown in the middle chamber 24 inFIG. 2, and an insulated vibrating device 34. Since each of thecompartments 24 are substantially the same as the others, the samenumerals will be considered to refer to similar components in each ofthe compartments 24 unless otherwise designated. Products 20 aretransferred into and out of each of the divided screening compartments24 through transfer doorways 36 by transfer mechanisms 38, as best seenin FIG. 6 and which will be described in more detail below. Automatedactuator arms 40, as shown in FIGS. 3, 4, and 9-12, permit electricalconnections to be established with the products 20 during screening sothat the products 20 can be put through electrical test proceduresconcurrent with the vibration and thermal stresses applied by theapparatus of this invention. The system is controlled from an operationconsole 42.

Referring again to FIGS. 1 and 2, the screening system of the presentinvention comprises a series of individual divided screeningcompartments 24, each of which is supported by a platform 44 having anumber of interconnected supporting legs 46 and braces 48. As shown inFIG. 2, the compartments 24 comprise a plurality of insulated walls 50,which isolate each divided screening compartment 24 from the ambientenvironment and from adjacent compartment 24. Each individual dividedscreening compartment 24 is accessible by a user through access doorways52 in the lateral sides 50 of each compartment 24, which doorways 52 canbe selectively closed and sealed with access doors 54 (FIG. 1). Thecompartments 24 are also equipped with the transfer doorways 36 whichinterconnect the interiors of the adjacent compartments 24 with eachother and with the ambient environment in a manner that accommodatesmovement of the products 20 sequentially into and out of adjacentchambers 24. The transfer doorways 36 are selectively opened or closedand sealed by vertically sliding doors 56, as best seen in FIG. 2.

Each compartment 24 can be equipped with temperature control apparatus,such as a heating device 30, as shown in the first and last compartment24 in FIG. 2, and/or a cooling device 32, as shown in the middle chamber24 of FIG. 2. Each chamber 24 can also have a circulating fan 58, cornerbaffles 60, and a channelling baffle 62 to control the exchange ofthermal energy with the products 20 that are being screened. Eachcompartment 24 also includes a vibrating device 34 to expose products 20to vibrational stresses. The transfer mechanism 38, shown in FIGS. 3-6and described in more detail below, in each of the compartments 24transfers products 20 into and out of each chamber or compartment 24.The actuator arm 40, shown in FIGS. 3-5 and 9-12 and described in moredetail below, allows the product 20 to be connected electrically with anelectronic function testing device (not shown) while the product 20 ispositioned in a compartment 24, as will also be further described below.

As shown in FIGS. 1, 2, and 3, the insulated walls 50 of the dividedscreening compartments 24 include lateral side walls 64 (FIG. 1),transverse side walls 66, an upper wall 68 and a lower wall 70, each ofwhich are comprised of a shell 72 of a rigid structural materialsurrounding a core 74 of insulating material. The shell 72 in thepreferred embodiment is made of stainless steel, which is durable,resists corrosion and is easy to clean. The insulating core 74 iscomprised of materials resistant to conduction of thermal energy, andconsequently the core 74 resists transmission of thermal energy betweenadjacent chambers or compartments 24 and/or the outside environment. Theinsulating material 74 also resists transmission of acoustic waves sothat noise generated within the compartments is insulated from theambient environment. The core 74 includes an inner layer 76 preferablyof fiberglass, which provides thermal insulation as well as some degreeof acoustic insulation, and an outer layer 78 preferable of avisco-elastic damping material, which provides additional acousticinsulation by damping vibration of the outermost layer of the shell 72.A suitable visco-elastic material is manufactured by Kinetics West, 7059South Curtice Street, Littleton, Colo. 80120, under the product name"AAP Damping Sheets with 1/4 inch foam and No. 1 barrier." Thismulti-layered thermal and acoustic insulation/barrier 74 is presentlyused in screening chambers manufactured by the QualMark Company, 1343West 121st Avenue, Denver, Colo. 80234, marketed under model numbersOSV-1, OSV-2, OSV-3 and OSV-4.

Both lateral side walls 64 of the divided screening compartments 24include manual access doorways 52 which are fitted with the manualaccess doors 54 to selectively open or close and seal the compartments24. The manual access doorways 52 allow manual access to the interior ofthe compartments 24 and facilitate construction and maintenance of thecompartments 24 (FIGS. 1 and 3). The manual access doors 54 have thesame structure as the compartment walls 50, comprising a shell 72 ofrigid structural material surrounding a core 74 ofinsulating/barrier/damping material 76 and 78. The access doors 54 aremounted to the lateral side walls 64 of the compartments 24 with hinges80 and are secured in a closed position by releasable latches 82. Theedges 84 of the access doors 54 are fitted with seals 86 (FIG. 3) tosecure the isolation of each compartment 24 from the ambientenvironment.

Each access door 54 is fitted with a transparent viewing window 88 toallow visual monitoring of the compartment 24 from outside. In thepreferred embodiment, each window 88 comprises multiple panes 89, asbest seen in FIGS. 3 and 8. The multi-pane windows 88 have unequalspacing between panes 89 so as to stop certain discrete frequencies ofsound from propagating through the multi-pane windows 88 via standingwaves, whereas propagation of waves of such frequencies would bepossible if the spaces between each of the panes 89 were equal (FIG. 8).Particularly, in the preferred embodiment, seven panes 89 are used,spaced at intervals relative to a base unit of measure at a relativespacing of 1.0, 1.1, 1.2, 1.3, 1.4 and 1.5 units, commencing from eitherthe innermost or outermost pane. By using unequal interpane spaces,standing waves are avoided and better overall reduction in soundtransmission results.

Transfer doorways 36 are formed in each of the transverse side walls 66of each compartment 24 with the doorways 36 being selectively openableor closeable and sealable with the sliding doors 56 as best shown inFIGS. 2 and 6. The sliding doors 56 are formed similarly to the walls64, 66, 68, 70 of the compartments 24 and the access doors 54,comprising a shell 72 of rigid structural material surrounding a core 74of insulating material. The sliding doors 56 are slidably received inrecesses 90 in the transverse side walls 66.

The sliding doors 56 are opened and closed by door actuators 92 (FIGS. 1and 2) comprising conventional pneumatic lifting devices mounted on anupper edge 94 of each of the transverse side walls 66. The dooractuators 92 each include a power cylinder 96 having a cylinder body 98mounted on the upper edge 94 of the associated transverse side wall. Anassociated piston rod 100 extends downwardly into the recess 90 of theassociated transverse side wall 66 and is operatively connected to asliding door 56. The power cylinders 96 are actuated by gas pressuresupplied through pressure couplings 102, which connect the powercylinders 96 with a gas pressure source (not shown). Reciprocaloperation of the power cylinders 96 thereby selectively moves thesliding doors 56 vertically between open and closed positions. The dooractuators 92 are controlled from the operation console 42.

The transfer doorways 36 are fitted with a pair of peripheral door seals104, shown in FIG. 6, which extend around opposing faces of eachtransfer doorway 36. The seals 104 are hollow and are inflatable withpressurized gas when the doors 56 are in the dosed position, the gaspressure being supplied from a gas pressure source (not shown) throughpressure couplings (not shown). The gas pressure, of course, causes theseals 104 to expand to securely engage opposite sides of the slidingdoor 56 to hermetically seal the associated compartment 24, therebyensuring the integrity of the insulation between adjacent compartments24 and the ambient environment. Correspondingly, the seals 104 can bedeflated by releasing the gas pressure from the seals 104, therebyloosening the engagement of the seals 104 against the sliding doors 56to allow the sliding doors 56 to be moved more freely.

Each compartment 24 incorporates a heating device 30 or a cooling device32, as shown in FIG. 2. These devices 30 or 32 heat or cool theatmosphere of each compartment 24 by exchanging thermal energy withwhatever gas is in the chamber 24. In the preferred embodiment, theheating devices 30 are heating coils and are mounted on the upper walls68 of the outermost compartments 24. The heating coils of device 30 areof a known type comprising electro-resistive coils which generate heatwhen electrical current is circulated through them. The heating devices30 are controlled in a conventional manner from the operation console42. The cooling device 32 in the preferred embodiment is mounted on theupper wall 68 of the center compartment 24 and comprises an input valve106 adapted to selectively introduce a low-boiling point fluid, such asliquid nitrogen, directly into the compartment 24. The liquid nitrogencan be supplied from a conventional pressurized canister 108 (FIG. 1)suspended from one lateral side 66 of a screening compartment 24. Theinput valve 106 is also controlled in a conventional manner from theoperation console 42. Liquid nitrogen introduced into the compartment 24boils or flashes immediately into its gaseous state. The boiling of theliquid nitrogen absorbs heat of vaporization from the atmosphere of thecompartment 24 and from the product 20 in the compartment 24.Beneficially, the boiling and expansion of the nitrogen also displacesany moisture which may have accumulated on the surface of the product 20in the compartment 24. However, because-the transition of the liquidnitrogen from its liquid to gaseous state involves a tremendousexpansion in volume, an exhaust pipe 110 is provided through the upperwall 68 of the center compartment 24 to allow the release of the gaspressure as necessary. In order to minimize the noise attending theexpansion and release of the nitrogen from the center compartment 24, aswell as noise emanating from the vibrating device 34 within the chamber24, a multi-baffled muffler 112 is fitted to the exhaust pipe 110.

The release of gas pressure through the exhaust pipe 110 is controlledby a one-way flapper valve 114, which allows gas to pass only from thecompartment 24, not into the compartment 24. If the gas pressure withinthe compartment 24 were to drop below the atmospheric pressure of theambient environment and gas were permitted to flow from the ambientenvironment into the compartment 24, which has been cooled by theintroduction of the low boiling point fluid, moisture inherent in theambient environment would flow into the chamber 24, potentiallyresulting in condensation and freezing of the moisture within thecompartment 24. Build-up of such condensation and/or freezing of themoisture within the chamber or compartment 24 could negatively impactthe product 20 being tested and various devices within the compartment24, thereby hampering screening and potentially damaging the product 20.

The flapper valve 114, best shown in FIG. 7, includes a lower coverpiece 116 and an upper cover piece 118 which are fitted to close twospaced apart openings 120, 121 in a valve chamber 122 of the exhaustpipe 110. Each cover piece 116, 118 is secured to horizontal dividingwalls 124, 125 within the valve chamber 122 at one end by respectivehinges 126, 127. Each of the openings 120, 121 in the valve chamber 122is fitted with a gasket 128, 129, respectively, to securely seal theopenings 120, 121 in the valve chamber 122 when the cover pieces 116,118 are in a closed position. The cover pieces 116, 118 are connected bya rigid coupling rod 130 joining respective pivotal joints 132, 133 onthe upper surface of the lower cover piece 116 and the underside of theupper cover piece 118, the coupling rod 130 ensuring movement of thecover pieces 116, 118 in unison with each other. The opening and closingof the upper cover piece 118 is controlled by a servo-motor 134controlled from the operation console 42 (FIG. 1). The opening andclosing of both cover pieces 116, 118 thus can be selectively controlledin response to the gas pressure measured within the chamber 24 by apressure transducer 136 mounted within the chamber 24, as shown in FIG.7, to maintain the gas pressure within the compartment 24 close to theatmospheric pressure of the ambient environment to prevent gas fromflowing back into the compartment 24. The opening and closing of thecover pieces 116, 118 can be conventionally automatically controlled inresponse to the level of gas pressure in the chamber 24 measured by thepressure transducer 136.

When using a plurality of divided screening compartments 24 in sequence,it is important to note that the last compartment 24 positioned beforethe exit conveyor 28 (FIGS. 1 and 2) should preferable employ a heatingdevice 30 and thereby be a hot chamber. If the last compartment 24 werea cold compartment, potentially undesirable condensation could form onthe products 20 once the products 20 are returned to the ambientenvironment.

Cooling and heating within the compartments 24 are controlled andenhanced by the circulating fans 58 (FIGS. 2 and 3). Circulating the gaswithin the compartments 24 accelerates heating or cooling of the gaswithin the compartment 24 by increasing contact between the gas and theheating device 30 or the cooling device 32. Similarly, circulation ofthe gas in the compartments 24 enhances the imparting or absorbing ofthermal energy between the gas and the product 20 in a compartment 24.The rate of transfer of thermal energy to the products 20 in thecompartments 24 can be controlled by regulating the speed of thecirculating fans 58, as well as controlling the amount of heating andcooling emanating from the respective devices 30,32, as described above.The circulating fans 58 are controlled from the operation console 42.

Circulation of the gas in the compartments 24 is also enhanced by cornerbaffles 60 and channeling baffles 62 (FIG. 2) within each compartment24, which optimally direct the flow of gas within the compartment 24.Both the corner baffles 60 and channeling baffles 62 preferably extendthe full interior width of each compartment 24. The curved cornerbaffles 60 mounted in upper corners of each compartment 24 reduce theturbulence and fluid friction of the flow of gas within each compartment24, which otherwise would be restricted by the opposing surfaces of thewalls of the compartment 24 meeting at a corner. The channeling baffles62 suspended from the upper walls 68 of the compartments 24 by bafflesupports (not shown) similarly enhance the circulation of gas. Each ofthe channeling baffles 62 has a flat mid-potion 138 terminating withcurved edge portions 140. The flat mid-portion of the channeling baffle62 aids in directing the gas in the compartment 24 in a cyclical flowdriven by the circulating fan 58. The curved edge portions 140 of thechanneling baffles 62 preferably have approximately the same curvatureas the corner baffles 60 in the plane of the lateral side walls 64 inorder to facilitate a smooth, cyclical flow of gas around the interiorof each compartment 24.

Each compartment 24 also incorporates a vibrating device or shaker table34, as best seen in FIGS. 2, 3, and 5. The vibrating device 34optionally is used to impart vibration to the product 20 being screened.As shown in FIG. 5, the vibrating device 34 includes a mounting platform142, which supports a pallet 22 that in turn holds the product 20 beingscreened. In the preferred embodiment, the mounting platform 142 ishollow and includes a plurality of vacuum ports 144, which assist insecuring the pallet 22 to the mounting platform 142 by vacuum pressureapplied through the vacuum ports 144. The mounting platform 142 of thevibrating device 34 has a hollow interior 146 (FIG. 5) in communicationwith the vacuum ports 144 and a source of vacuum (not shown) connectedto the vacuum ports 144 through pressure couplings 148. The operation ofthe vacuum ports 144 is controlled at the operation console 42.

The mounting platform 142 is generally supported from the lower wall 70of each compartment 24 by a plurality of resilient support elements 150(FIG. 2). These resilient support elements 150, comprising springs inthe preferred embodiment, support the weight of the mounting platform142, the pallet 42, and any product 20 mounted thereto, but do notimpede the vibration generated by the vibrating device 34.

Vibration is generated by a plurality of exciters 152 (FIG. 2) rigidlyattached to the underside 154 (FIG. 5) of the mounting platform 142. Theexciters 152, shown in FIGS. 2 and 3, in the preferred embodiment areconventional pneumatic vibrators. The pneumatic vibrators 152incorporate an enclosed cylinder housing 156, a free floating piston(not shown) therein and pressure couplings 158 connecting the cylinder156 with a source of gas pressure (not shown). The repeated collisionsof the free piston (not shown) with the cylinder housing 156 impartshock pulses to the cylinder housing 156, thereby imparting vibration tothe cylinder housing 156 and to the platform structure 142 connectedthereto. In this case, the vibrations are imparted to the mountingplatform 142 and, in turn, to the pallet 22 and the product 20positioned on the platform 142. The amount of vibration can becontrolled by regulating the gas pressure supplied to the exciter 152from the gas pressure source. Multiple exciters 152 can be employed toimpart vibrations to the mounting platform 142 in one or more axes toprovide universal vibrational motion to the product 20. Vibratingdevices or exciters 152 of the type mounted in screening chambersmarketed by the QualMark Company (reference above) under model numbersOSV-1, OSV-2, OSV-3 and OSV-4 have been found suitable for thisapparatus, although a variety of suitable exciters are available fromnumerous manufacturers as is well-known to persons skilled in this art.

In screening the products 20, it is not necessary to heat and cool thevibrating device 34. Accordingly, the upper surface 160 of the mountingplatform 142 can be covered with an insulating layer 162 (FIG. 5), whichlimits the exchange of thermal energy between the mounting platform 142and the gas in the compartment 24 as well as between the mountingplatform 142 and the pallet 22. In the preferred embodiment, theinsulating layer 162 is comprised of a fluorosilicon rubber, which notonly restricts the exchange of thermal energy between the mountingplatform 142 and the pallet 22 mounted thereon, but also provides aslip-resistant surface to aid in maintaining positioning of the pallet22 on the mounting platform 142. The insulating layer 162 does not coverthe vacuum ports 144.

Moreover, to insulate the support elements 150 and exciters 152, eachcompartment 24 is divided into a testing chamber 164 and a controlchamber 166 by an elastic boot or diaphragm 168 (FIG. 3 and 5), whichextends between and joins the mounting platform 142 to the lateral sidewalls 64 and transverse side walls 66 of each compartment 24. Thediaphragm 168 is joined to the walls 64, 66 by a molding strip 170 (FIG.5). The diaphragm 168 prevents gas from flowing from the testing chamber164 into the control chamber 166, thereby insulating the supportelements 150 and exciters 152 (FIG. 2) from the testing chamber 164.However, the diaphragms 168 are sufficiently resilient so as not todampen the vibration imparted by the vibrating device 34. Accordingly,the diaphragm 168 minimizes the waste of energy in heating and/orcooling the vibrating device 34. Furthermore, because the diaphragm 168prevents gas from flowing from the testing chamber 164 into the controlchamber 166, the diaphragm 168 aids in maintaining the cyclicalcirculation of the gas in the testing chamber 164 as facilitated by thecorner baffles 60 and channelling baffles 62.

Each compartment 24 also includes a transfer mechanism 38, as best shownin FIG. 6. Once a screening cycle has been completed in a compartment24, the transfer mechanism 38 transports the pallet 22 on which theproduct 20 is mounted into the next compartment 24 or onto the exitconveyor 28 (FIGS. 1 and 2). Specifically, the transfer mechanism 38 inthe preferred embodiment comprises pairs of rolling devices in thenature of endless-belt type conveyors or tractors 172 (FIGS. 4, 5, and6), which are retractably-mounted for vertical reciprocative movementadjacent opposite lateral sides of the mounting platform 142 and beneathopposite sides of the pallet 22 disposed on the mounting platform 142,but above the diaphragm 168. The tractors 172 are supported by pairs ofextendable pneumatic power cylinders 174, one power cylinder 174 at eachend of a tractor 172, and each power cylinder 174, comprising a cylinderbody 176 and an extendable piston rod 178. The cylinder bodies 176 aremounted on the lower wall 70 of each compartment 24, and the piston rods178 sealingly extend through openings 180 in the diaphragm 168 (FIG. 5)for connection to the tractors 172. The power cylinders 174 are operatedthrough a gas pressure source (not shown) connected to the powercylinders 174 through pressure couplings 182. The tractors 172 aredeployed by extending the piston rods 178 in unison and thereby raisingthe tractors 172, causing the tractors 172 to engage the undersurface ofan aligned pallet 22, as shown in FIG. 5, and lift the pallet 22 withthe product 20 supported on the pallet 22 from the mounting platform142.

As best seen in FIGS. 5 and 6, each of the tractors 172 comprises a pairof pulleys 184 rotatably mounted on a shaft 185 supported in a frame187. One of the pulleys 184 is driven by a motor 186 (FIG. 5), while theother pulley 184 is passively rotatable. The pulleys 184 support anendless belt 188 whose underside 190 engages the outer surfaces 192 ofthe pulleys 184. When the tractor 172 is activated, the motor 186rotates the associated pulley 184, causing the endless belt 188 torotate around the pulleys 184. Thus, once the tractors 172 areextendably deployed or raised to engage a pallet 22, the endless belts188 engage the undersurface of the pallet 22, and the rotation of theendless belts 188 roll the pallet 22 toward its next destination, eitherto the next compartment 24 or to the exit conveyor 28 (FIGS. 1 and 2).

Forward movement of the pallets 22 is controlled by pneumaticallyretractable stops 194 as best seen in FIGS. 4 and 6 positioned betweenthe forward ends of the left and right tractors 192. The stops 194 eachcomprise a stop prong 196 mounted atop a pneumatic power cylinder 198.The cylinder 198, as best seen in FIG. 6, includes a cylinder body 200and an extendable piston rod 202. The cylinder body is verticallymounted on the mounting platform 142. The power cylinder 198 is operatedthrough gas pressure provided by a gas pressure source (not shown)through pressure couplings (not shown). The power cylinder 198 causesthe piston rod 202, which sealingly extends through a stop opening 204in the diaphragm 168, to extend the stop prong 196 upwardly to engagethe pallets 22 when they are being moved by the tractors 172. The stops194 are controlled from the operation console 42, and they engage thepallets 22 to inhibit and selectively stop forward translationalmovement of the pallets 22. An electrical sensor (not shown) may befitted on the stop prong 196 to generate a signal to the operationconsole 40 that the pallet 22 has contacted the prong 196, and thetractors 172 are then deactivated.

The motion of the pallets 22 is also governed by guide rails 206, whichposition the pallets 22 in the compartments 24, as shown in FIG. 4.There are two guide rails 206 in each compartment 24, one on each sideof the path to be followed by the pallets 22 as they move through thecompartment 24. The guide rails 206 are mounted on support braces 208secured to the inside surfaces of the access doors 54, the access doorsdefining part of the lateral side wall 64 of each compartment 24, asdescribed above. The guide rails 206 are mounted at a predeterminedheight above the plane of the mounting platform 142 as shown in FIG. 5.They are spaced from each other a distance slightly greater than thewidth of a pallet 22 to help guide the pallet 22 into and out of theassociated compartment 24 while allowing for vibrational movement of thepallet 22 such as imposed by a vibrating device 34 (FIG. 2). Each guiderail 206 has oblique end portions 210 flared outwardly from a straightcenter portion 212, as best seen in FIG. 4. The oblique end portions 210present a flared opening between the guide rails 206 juxtaposed onopposite sides of compartment 24, which receives the pallets 22 as theyare transported into the compartment 24. The oblique end portions 210channel the pallets 22 into the center of the compartment 24, ifnecessary, where the pallets 22 are guided into place by the straightcenter portions 212 of the guide rails 206, facilitating controlledpositioning of the pallets 22.

The controlled positioning of the pallets 22, as described above,facilitates comprehensive screening by electrical testing devices (notshown) of products 20, including electrical components. Each of thepallets 22 can be fitted with an electrical receptacle 214, as shown inFIGS. 5, 9, and 11, which receives one end of a set of electricalconnectors 216. At the other end of the connectors are plugs 218 (FIG.5), which are matched to electrical sockets 220 (FIG. 5) of the typesometimes found on products 20. The connectors 216 permit electricalcommunications to be established between the product 20 and thereceptacle 214, which in turn permits communication with a testingdevice (not shown) that is a source of electrical communications.Specifically, the connectors 216 allow the exchange of power, controlsignals, and other electrical transmissions with the product 20 beingscreened. The plugs 218 are attached to the mating sockets 220 on theproduct 20 when the product is first mounted on its associated pallet 22prior to entering the compartments 24.

As shown in FIGS. 9-12, the receptacle 214 has a test plug jack 222adapted to receive a test plug 224 and two guide pin sockets 226 adaptedto receive guide pins 228 for directing the test plug 224 into place.The test plug 224 has a tapered back end 230 used for orienting the testplug as will be explained below. The test plug 224 is connected to atesting device as mentioned above, by flexible conductors 232. The testplug 224 is engaged and disengaged with the receptacle 214 by anactuator arm 40, to which the test plug 224 is permanently attached.

In the preferred embodiment, the actuator arm, generally depicted inFIGS. 3, 4, and 5, and 9-2 as 40, comprises a firsthorizontally-reciprocating power cylinder 234 (FIGS. 5, 10, and 12) anda second horizontally-reciprocating power cylinder 236 (FIGS. 5 and9-12). The first cylinder 234 has a cylinder body 238 mounted on theinside of the access door 54. Similarly, the second cylinder has acylinder body 240 mounted on the inside the an access door 54 mounteddirectly above the first horizontally-reciprocating cylinder 234. Thefirst cylinder 234 includes an extendable piston rod 242 which supportsa test plug guide plate 244. The guide plate 244 includes a base plate246, which supports a guide plug bracket 248 and the two tapered guidepins 228. The guide plug bracket 248 releasably receives the taperedback portion 230 of the test plug 224 when the test plug 224 is in theretracted position. The back portion 230 of the test plug 224 and thetest plug bracket 248 are shaped to ensure that the test plug 224 isproperly oriented to engage the receptacle 214 when the actuator arm isdeployed to engage the test plug 224 with the receptacle 214. The secondpower cylinder 236, which is used to remove the test plug 224 from thereceptacle 214, includes a piston rod 250 connected to a spring 252,which in turn is connected to the back end 230 of the test plug 224through an opening 254 in the back of the guide plug bracket 248.

To engage the test plug 224 with the test plug jack 222 on thereceptacle 214, the first power cylinder 234 and second power cylinder236 are extended simultaneously (FIG. 12). The guide pins 228 on theguide plate 244 are received in the tapered guide pin sockets 226 in thereceptacle 214 on the pallet 22, and, as the guide plate 244 is furtherextended, the tapered pins 228 securely engage the openings 226 toposition the test plug 224 over the test plug jack 222 on the receptacle214. Thus, once the first power cylinder 234 has reached full extension,the guide pins 228 have positioned the test plug 224 to connect with thetest plug jack 222 on the receptacle 214, and the test plug 224 isinserted into the jack 222. The first cylinder 234 is then retracted(FIG. 9), withdrawing the guide plate 244 from the receptacle 214, whilethe second cylinder 236 is left extended. Accordingly, the test plug 224is left connected to the receptacle 214 on the pallet 22, maintainingelectrical communication between the product 20 and the testing device(not shown), and the actuator arm 40 remains flexibly connected with thetest plug 224 via the spring 252. Accordingly, once the vibrating device34 is activated, no rigid members of the actuator arm 40 will impede thevibration imparted by the vibrating device 34.

Once the test phase has been completed and the vibrating device 34 hasbeen deactivated, the first cylinder 234 is m-extended (FIG. 12), theguide pins 228 on the guide plate 244 engaging the guide pin sockets 226in the receptacle 214, and the test plug bracket 248 receiving thetapered back 230 of the test plug 224. Both the first power cylinder 234and second power cylinder 236 are then simultaneously retracted, thefirst cylinder 234 pulling the guide plate 244 away from the receptacle214, and the second cylinder 236 pulling the test plug 224 out of thejack 222 on the receptacle 214 (FIGS. 10-11). This process issubsequently repeated for successive test phases.

The engagement of the test plug 224 with the receptacle 214 completesthe connection between the product 20 being screened and the testingdevice (not shown). It should be noted that the testing device maysubject the product 20 to additional stresses by introducing a range ofnormal or unanticipated stimuli through power cycling, voltage changes,and input power frequency variations. Such testing devices are known inthe art.

The entry conveyor 26 and exit conveyor 28 (FIGS. 1 and 2) allow thepallets 22 to be introduced into and removed from the compartments 24through the transfer doorways 36. In the preferred embodiment, the entryand exit conveyors 26, 28 are comprised of a number of selectivelydriven parallel rollers 256, the axes of which extend transversely ofthe conveyors 26, 28 and lie in a plane parallel with the surfaces ofthe conveyors 26, 28. The axes of the rollers 256 are also parallel to,and aligned vertically with, the base edge of the transfer doorways 36at opposite ends of the apparatus. The rollers 256 are rotatably mountedin a conveyor frame 258, which is supported by a number of support legs260. The rollers 256 permit translational movement of the pallets 22toward and away from the compartments 24, but they do not permitmovement of the pallets 22 along the axes of the rollers transverse tothe conveyors 26, 28. In the preferred embodiment, the rollers areselectively powered by motors (not shown) to motivate the pallets 22toward and away from the series of compartments 24.

The entry conveyor 26 may be equipped with a bar code reader 262 mountedon the conveyor frame 258 at a height even with the pallets 22 when theyare positioned on the surface of the entry conveyor 26. Accordingly, thebar code reader 262 is positioned to read bar codes 264 affixed to thepallets 22. The reader 262 may be a passive reader, which reads the codeas the bar codes 264 pass by the reader 262, or the reader 262 may be anactively scanning type, which can also read the bar codes 264 when thebar code 264 and the reader 262 are stationary relative to each other.The bar code reader 262 is electrically connected to the operationconsole 42. In the preferred embodiment, the bar codes 264 are used toencode information concerning the product 20 being screened. The encodedinformation may include a tracking number for the particular product 20,product type information which corresponds to a predetermined screeningsequence stored in the operation console 42, or other pertinentinformation.

Products 20 to be screened are mounted on specially-designed pallets 22.The pallets 22, as shown in FIGS. 4 and 5, serve as a generalized,transportable platforms for products 20 to be screened. The pallets 22are primarily composed of rigid, lightweight material. Further, aspreviously described and shown in FIG. 3, each pallet 22 may be fittedwith a receptacle 214 and electrical connectors 216 facilitatingelectrical interaction with the product 20 to be screened. Each pallet22 also may bear bar codes 264 identifying the attached product 20.

The pallets 22, which are best seen in FIGS. 4 and 5, have an upperplanar surface 266, providing a versatile surface for supportingproducts 20 to be screened. A lower surface 268 of the pallet has planaredge surfaces 270 which extend beyond the dimensions of the mountingplatform 142 and facilitate transport of the pallet 22 by the tractors172, which are engageable with the lower edge surfaces 268, 270 of apallet 22 from beneath. Within the dimensions of the mounting platform142, however, the lower surface 268 of the pallet contains a recess 272,which facilitates the generation of a secure vacuum seal on the pallet22 by the vacuum ports 144. Structural support of the pallet isbuttressed by a number of support standoffs 274 extending from therecess 272, which engage the surface of the mounting platform 142. Thepositioning of the standoffs 274 does not coincide with the positioningof the vacuum ports 144 so as not to interfere with their operation.Planar side surfaces 276 on the pallets 22 allow the sides to be guidedby the guide rails 206 to direct the motion of the pallets 22. Theplanar side surfaces 276 also facilitate the labelling of the pallets 22with bar codes 264 (FIG. 1) relating to the product 20 mounted thereon,as described above.

Ideally, the pallets 22 provide both a rigid platform for supportingproducts 20 to be screened and have minimal impact on heating and/orcooling of the products 20 mounted thereon. Consequently, the pallets 22are ideally composed of materials which have a high rigidity per unitmass. The materials must be rigid in order to support the products 20which the pallets 22 will carry, to facilitate various means ofattaching the product 20 to the pallet 22, as will be discussed below,and to readily transmit to the products 20 mounted thereon vibrationsgenerated by the vibrating devices 34. Further, materials which have ahigh rigidity per unit mass allow for rigid pallets 22 which arelightweight to minimize the overall weight that must be borne by theapparatus. Because the amount of thermal energy a body may radiate orabsorb is proportional to its mass, it is desirable that the pallets 22have the minimum possible mass in order to minimize the impact of thepallets 22 on heating or cooling the products 20 mounted thereon. In thepreferred embodiment, aluminum and magnesium are well-suited as pallet22 materials.

In order to further minimize the impact of the pallets 22 on theexchange of thermal energy between the atmosphere of the testingchambers 164 and the products 20 to be screened, the upper surface 266and side surfaces 276 of the pallets 22 are preferably covered with alayer of insulating material 278. In the preferred embodiment, theinsulating material 278 is a fluorosilicon rubber. The fluoro-siliconrubber layer 278 resists transmission of thermal energy, and provides askid-resistant surface to aid in maintaining the positioning of aproduct 20 on the pallet 22. If desired, additional insulation (notshown) may be layered over the upper surface 266 and side surfaces 276of the pallet 22 to further resist the exchange of thermal energybetween the testing chamber 164 and the pallet 22. These layers can beformed to fit around the product 20 being screened so as to insulate thepallet 22 without insulating the product 20 being screened.

In the preferred embodiment, the products 20 are mechanically fastenedto the pallets 22 by clamps 280 (FIG. 5), but they may also be securedto the pallets 22 by banding or any other technique appropriate to thesize, shape, and nature of the product 20, which will ensure the product20 will remain secured to the pallet 20 throughout screening.

The overall operation of the environmental screening system iscontrolled from an operation console 42 (FIG. 1). The console 42comprises control switches, control logic and monitoring devicesnecessary to implement and monitor the operation of the screeningsystem, including the entry conveyor 26, the exit conveyor 28, theheating devices 30, the cooling device 32, the vibrating devices 34, thetransfer mechanisms 38, the circulation fans 58, the door actuators 92,the flapper valve 114, and the gas pressure sources (not shown). Theoperation console 42 can be manually-operated or automated in accordancewith skills known in the art to suit the particular application. At oneextreme, control of all the components may be controlled manually byswitches on the panel 42. At another extreme, the operation console 42may be entirely computer-controlled, and a pre-programmed screeningsequence might be initiated upon detection by the bar code reader 262 ofthe bar codes 264 imprinted of the pallets 22 which may correspond to apreprogrammed screening sequence.

The screening process comprises a number of steps. In the preferredembodiment, the process begins with securing the product 20 to a pallet22 with clamps 280, connecting any electrical sockets 220 on the product20 with plugs 218 attached to electrical connectors 216, whichelectrically connect the sockets 220 on the product 20 to the receptacle214 mounted on the pallet 22. Once the pallet 22 is loaded, the pallet22 is placed on the entry conveyor 26, and the entry conveyor 26 isactuated. The commencement of a new screening cycle may be manuallyactivated at the operation console 42 or may be preprogrammed, possiblyinitiated by the bar code reader 262 detecting bar codes 264 on thepallets 22, which represent preprogrammed screening sequences. Theinitiation of a screening cycle involves passing each of the products 20being screened to their next screening phase.

Generally, in each of the compartments 24, the circulation fan 58 isstopped to minimize transmission of thermal energy between thecompartments 24 and between the compartments 24 and the ambientenvironment when the sliding doors 56 are retracted to open doorways 36,thereby minimizing the exchange of thermal energy and resultingtemperature degradation between the compartments 24. The actuator arm 40is engaged to sever the electrical connections between the testingdevice and the product 20. The first cylinder 234 is extended, then boththe first cylinder 234 and the second cylinder 236 are retracted toremove the test plug 224, from the receptacle 214 on the pallet 22. Thevacuum ports 144 attaching the lower surface 268 of pallet 22 to thesurface of the mounting platform 142 are released. Subsequently, thepneumatic door seals 104 are deflated, and the door actuators 92 areactivated, retracting the sliding doors 56 into the recesses 90 in thetransverse side wills 66 to open the doorways 36. The transfer mechanism38 is deployed by the power cylinders 174, lifting the pallet 22 fromthe mounting platform 142, and the pallet 22 is then rolled by thetractors 172 through the next transfer doorway 36 to transfer the pallet22 into the next compartment 24. The next pallet 22 on the entryconveyor 26, instead of being moved by the transfer mechanism 38, isrolled by the entry conveyor 26 into the initial compartment 24. In thecase of the last compartment 24, the transfer mechanism 38 lifts thepallet 22 from the compartment 24 and rolls it onto the exit conveyor28.

Once the pallet 22 has encountered the stop 194 indicating that thepallet 22 has reached a predetermined, desired location within thecompartment 24, the transfer mechanism 38 is retracted. The slidingdoors 56 are closed by the door actuators 92, and the door seals 104 areinflated. The vacuum ports 144 are engaged to attach the pallet 22 tothe mounting platform 142, and the actuator arm 40 is extended to allowthe test plug 224 on the actuator arm 40 to engage the receptacle 114 onthe pallet 22. The heating device 30 or cooling device 32 is activatedto reach or restore the desired temperature in the testing chamber 164,and the circulation fan 58 is activated. The vibrating device 34 isactivated as desired. Ideally, these steps are all automaticallysequenced and closely synchronized in order to minimize the breach ofthermal integrity in each of the compartments 24 when the sliding doors56 are opened.

The independence of the compartments 24 is significant. For example, thetesting chamber 164 in one compartment 24 may be heated to a hightemperature, and the testing chamber 164 in the adjacent compartment 24cooled to a very low temperature in order to achieve the most rigorousthermal shock test possible. In addition, one compartment 24 may employa shaker table 34 vibrating very actively, whereas in the nextcompartment 24 the shaker table 34 may only be minimally activated ornot activated at all. Any desired combination of thermal and/orvibrational stresses can be introduced in this manner.

As can be appreciated with this detailed description, the presentinvention allows more comprehensive environmental screening thanconventional techniques, and makes environmental screening moreefficient by reducing the time, manual intervention and energy requiredto undertake environmental screening. Products 20 can be morecomprehensively screened under multiple environmental stimuli, includingtemperature changes, vibration and other stresses. Further, theenvironmental screening can be accomplished with greater efficiency. Thetesting chambers 164 in the compartments 24 are maintained at desiredtemperatures so that only the products 20 themselves need be heated orcooled to proceed with the screening, and the entire compartment 24 neednot be heated or cooled with each screening cycle, saving time andenergy. Further, products 20 can be moved between compartments andconnected to the screening apparatus with little or no manualintervention, rendering such screening more cost effective.

A presently preferred embodiment of the present invention and many ofits improvements have been described with a degree of particularity.This description has been made by way of preferred example. It should beunderstood, however, that the scope of the present invention is definedby the following claims, and not necessarily by the detailed descriptionof the preferred embodiment.

The invention claimed is:
 1. Environmental screening apparatus forscreening a product under different screening conditions, comprising:aplurality of testing compartments positioned in an array in relation toeach other, each of said compartments having an entrance doorway and anexit doorway with a thermally insulated separating adjacent compartmentsin the array, each of said walls having a doorway opening that is boththe exit doorway in one of the compartments and the entrance doorway inan adjacent compartment; openable and closeable door means positioned ineach of said doorway openings for alternately opening and closing saiddoorway openings; temperature control means in each compartment forproviding a unique temperature environment in each compartment; palletmeans for mounting and carrying the product sequentially through thecompartments in the array; vibrating means in said compartments forimparting vibrating motion to said pallet means; and transfer meansoperatively engageable with the pallet means for transporting the palletmeans and the product mounted on the pallet means between thecompartments when the door means have opened said doorway openingsbetween said compartments.
 2. The apparatus of claim 1, wherein thetemperature control means in at least one of said compartments includesa gas expansion nozzle for introducing a volatile liquid under pressureinto the compartment to flash evaporate and cool the compartment byabsorbing heat of vaporization, and exhaust means for exhausting excessgas from the compartment to the ambient environment, said exhaust meansincluding a conduit extending from the compartment to the ambientenvironment with one-way valve means in said conduit for allowing gas toflow only out of the compartment through the conduit.
 3. The apparatussa defined in claim 2, wherein said exhaust means further includes amuffler comprising a series of baffles for dampening vibrations carriedby gas being released from the compartment.
 4. The apparatus of claim 2,wherein said one-way valve means includes a seat, a pivotal flapperclosure piece positioned to open and close on said seat, servo meansconnected to said flapper closure piece for pivoting said flapperclosure piece to open or closed position, transducer means for sensingambient pressure and compartment pressure, and control means connectedto said servo means and to said transducer means for causing said servomeans to close said flapper closure means onto said seat when ambientpressure exceeds compartment pressure.
 5. The apparatus of claim 4,wherein said one-way valve means includes two seats and two respectiveflapper closure pieces for opening and closing onto the two seats, andincluding a link rod connected between said two flapper closure piecesin a manner that causes the two flapper closure pieces to open and closein unison.
 6. The apparatus of claim 2, wherein the temperature controlmeans in the last compartment in the array includes heater means forheating said last compartment in the array to a temperature aboveambient temperature such that a product moving sequentially through thecompartment in the array is heated above ambient temperature in the lastcompartment after being cooled below ambient in a compartment precedingthe last compartment.
 7. The apparatus as defined in claim 1, whereinthe insulated walls and the door means have thermally insulated coresincluding at least one layer of fiberglass to resist transmittingthermal energy.
 8. The apparatus as defined in claim 1, wherein theinsulate walls and the door means have acoustically insulated coresincluding at least one layer of a visco-elastic damper material toresist transmission of vibrations.
 9. The apparatus of claim 8, whereinsaid acoustically insulated cores also include a sound decoupling layerof foam.
 10. The apparatus of claim 8, wherein said acousticallyinsulated cores also include a sound barrier layer.
 11. The apparatus asdefined in claim 1, wherein the temperature control means furthercomprises selectively controllable circulation means for enhancing theexchange of thermal energy between the temperature control means and thecompartment.
 12. The apparatus as defined in claim 11, wherein thecirculation means further includes a fan means for facilitating theexchange of thermal energy between the temperature control means and thecompartment.
 13. The apparatus as defined in claim 11, wherein thecirculation means further comprises baffling means to enhancecirculation within the compartment.
 14. The apparatus of claim 13,wherein said baffling means includes smoothly rounded air deflectorspositioned in corners where walls intersect.
 15. The apparatus of claim13, wherein said baffling means includes a partial partition extendingpartially across the compartment between the fan means and the palletmeans when the pallet means is positioned in the compartment.
 16. Theapparatus of claim 13, wherein said baffling means comprises curvedcorner baffles positioned in upper corners of the compartment.
 17. Theapparatus of claim 13, wherein said baffling means includes an elongatedwith curved lateral edges positioned to extend through the compartmentbetween said fan means and said vibrating means.
 18. The apparatus asdefined in claim 1, including:door actuator means for opening andclosing at least some of the door means; and door sealing meansreleasably at least some of the door means when the door means are inposition to close the doorway openings.
 19. The apparatus as defined inclaim 1, further including retraction means operatively associated withsaid transfer means for selectively removing and said transfer meansfrom engagement with the product when the product is being screened inthe compartment.
 20. The screening apparatus as defined in claim 1,further comprising an operation console operatively connected to thetemperature control means, the vibrating means, and the transfer means.21. The apparatus as defined in claim 20, wherein the pallet meansfurther comprises identifying indicia associated with the productsupported on the pallet means.
 22. The apparatus as defined in claim 21,further including means operatively connected the operation console andthe indicia on the pallet means whereby the operation console isoperative to respond to the identifying indicia on the pallet means. 23.The screening apparatus of claim 1, wherein said transfer means includestractor means for engaging said pallet means and causing said palletmeans to move into the compartment when the door means of the entrancedoorway is opened, for disengaging the pallet means when both the doormeans of the entrance doorway and the door means of the exit doorway areclosed with the pallet means in the compartment, and for engaging thepallet means and causing the pallet means to move out of the compartmentwhen the door means of the exit doorway is opened.
 24. The screeningapparatus of claim 23, wherein said tractor means includes a revolvingtrack belt configured with a path surface that is liftable intoengagement with a portion of the pallet means that is positioned overthe track belt and wherein revolving movement of the track belt isimparted to propel the pallet when the track belt is engaged with thepallet means.
 25. The screening apparatus of claim 24, includingretractable stop means in the compartment for extending into a path oftravel of the pallet means being propelled by the track belt to stopmovement of the pallet means in the compartment and for retracting fromthe path of travel to allow movement of the pallet means out of thecompartment.
 26. The screening apparatus of claim 23, including platformmeans positioned in said compartment adjacent said tractor means forsupporting said pallet means in said compartment when said tractor meansis disengaged from said pallet means.
 27. The screening apparatus ofclaim 26, including vacuum anchor means for anchoring said pallet meanspallet with vacuum in immovable relation to said platform means.
 28. Thescreening apparatus of claim 27, wherein said vacuum means includesports in said platform means adjacent the pallet means with a vacuumsource connected to the ports.
 29. The screening apparatus of claim 28,including a resilient, insulating, nonskid surface on the platform meansthat supports the pallet means.
 30. The screening apparatus of claim 26,including vibration means connected to said platform means for impartingvibrating motion to said platform means.
 31. The screening apparatus ofclaim 30, including a flexible diaphragm extending from the separatingsidewall of the compartment over the platform means and vibration meansand under the pallet means to divide the compartment into a firstthermal chamber and a second thermal chamber that is thermally insulatedfrom the first thermal chamber.
 32. The screening apparatus of claim 23,including a plurality of said compartments positioned adjacent eachother such that an exit doorway of one of the compartments is anentrance doorway of an adjacent compartment, and wherein said tractormeans of one of the compartments moves the pallet means a sufficientdistance to extend a portion of the pallet means out of said one of thecompartments and the adjacent compartment where said portion of thepallet means is engageable by tractor means in the adjacent compartment.33. The screening apparatus of claim 32, including environment controlmeans in each of said compartments for heating or cooling thecompartment in relation to the ambient environment.
 34. The screeningapparatus of claim 33, wherein the environment control means includes afan.
 35. The screening apparatus of claim 34, wherein the environmentcontrol means includes baffle means, positioned in the compartment fordirected air or other gas in the compartment that is being moved by thefan to distribute and mix throughout each compartment.
 36. The screeningapparatus of claim 23, including plug receptacle means on said palletmeans and plug means in the compartment for making an electricalconnection of electric test equipment to the pallet means, said productalso being electrically connectable to said plug receptacle means. 37.The screening apparatus of claim 36, wherein said plug means includesextension and retraction means for extending said plug means intoelectrical contact with said plug receptacle means and for retractingsaid plug means away from said plug receptacle means.
 38. The screeningapparatus of claim 37, wherein said extension and retraction meansincludes alignment means for aligning said plug means with said plugreceptacle means.
 39. The screening apparatus of claim 38, wherein saidalignment means includes a conical protrusion adjacent said plug meansand a conical socket adjacent said plug receptacle means for receivingsaid conical protrusion and thereby moving said plug means intoalignment with said plug receptacle means.
 40. The screening apparatusof claim 39, including guide extension and retraction means connected tosaid conical protrusion for extending and retracting said conicalprojection independent of said plug means.
 41. The screening apparatusof claim 1, including temperature control means in the compartment forheating or cooling the compartment and vibration control means forimparting vibrational movement to the pallet means.
 42. The screeningapparatus of claim 1, wherein each of said compartments includes anadditional thermally insulated wall that does not separate adjacentcompartment and that does not have and of said entrance doorways or exitdoorways, said additional thermally insulated wall including a windowcomprising multiple transparent juxtaposed panes positioned in spacedapart relation to define multiple spaces separated by said panes suchthat each of said spaces has a different distance between panes than theother spaces.
 43. The screening apparatus of claim 42, including sevenspaced apart panes that are spaced at intervals relative to a base unitof measure at a relative spacing of 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5units.
 44. The apparatus of claim 1, wherein said testing compartmentsare positioned in a linear array.